LoC: Genuine release

On November 28, 2003, two cases of Legionnaire’s Disease were recorded, the first symptoms of which dated back to the beginning of November. The dates of outbreak of the pathology, which were then staggered over time, revealed two distinct waves of contamination with a total of 86 individuals contaminated, aged between 32 and 92 (of whom 18 died).

These cases all broke out within a radius of slightly over 10 km around the city of Lens. The DDASS (local Sanitary and Social Affairs Office) conducted environmental investigations at the homes of patients and within several facilities open to the public. At the request of the DRIRE (Regional Agency for the Environment, Research and Industry), all facilities operating cooling towers within the designated zone were asked to adopt measures to identify the eventual presence of legionella and clean their circuits. On October 15, the operator of a chemical installation specialised in alcohols and fatty acids extracted samples whose results revealed a concentration of legionella at a level of 730,000 CFU units/litre. Following a shock treatment using biocides, analyses 15 days later yielded a concentration of less than 100 CFU/litre. On November 20, another inspection announced that the level of 600,000 CFU/litre had been reached.

In light of these results, the chemical plant’s cooling towers were ordered to be shut down on November 29. As of December 3, the tower circuits were drained and cleaned. Operations resumed on December 22, and a prefectural decree was issued January 2, 2004 mandating the operator to halt all plant activity once again due to the appearance of a second epidemic wave. High pressure cleaning work could have induced the dispersion of a contaminated aerosol. At the same time, the Prefect commissioned the DRIRE Agency to extend its investigations, notably by inventorying all cooling towers within the neighbouring 53 towns and imposed the shutdown of several installations (automobile washing stations, food processing activities, refrigerated warehousing, etc.), causing layoffs to hundreds of workers for several days. Even though a similarity was detected between the strains extracted from 23 of the patients and those present in the suspected cooling tower at the petrochemical plant, other sources of contamination could not be ruled out. High legionella counts in the lagoons of this same plant necessitated turning off aerators on January 20. This site’s revenue loss would amount to several millions of Euros, corresponding to a production downtime of 14 weeks. A prefectural order authorising reactivation of the towers was issued on March 19, 2004, yet the plant would never operate again.

Image credit: TF1

In the early hours of 3 December 1984 a relief valve on a storage tank containing highly toxic methyl isocyanate (MIC) lifted. A cloud of MIC gas was released which drifted onto nearby housing.

Prior to this, at 23.00 hrs on 2 December, an operator noticed the pressure inside the storage tank to be higher than normal but not outside the working pressure of the tank. At the same time a MIC leak was reported near the vent gas scrubber (VGS). At 00.15hrs a MIC release in the process area was reported. The pressure inside the storage tank was rising rapidly so the operator went outside to the tank. Rumbling sounds were heard from the tank and a screeching noise from the safety valve. Radiated heat could also be felt from the tank.
Attempts were made to switch on the VGS but this was not in operational mode.

Approximately 2,000 people died within a short period and tens of thousands were injured, overwhelming the emergency services. This was further compounded by the fact that the hospitals were unaware as to which gas was involved or what its effects were. The exact numbers of dead and injured are uncertain, as people have continued to die of the effects over a period of years.

The severity of this accident makes it the worst recorded within the chemical industry.

KEY ISSUES:
• PLANT MODIFICATION / CHANGE PROCEDURES
• REACTION / PRODUCT TESTING
• DESIGN CODES – PLANT
• MAINTENANCE PROCEDURES
• EMERGENCY RESPONSE / SPILL CONTROL

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The International Biosynthetics (IBIS) plant was, at the time of the accident, a wholly owned subsidiary of Shell UK Ltd. and employed some 250 people in the manufacture of fine chemicals.

The release occurred on the phosgene plant at 11:27 hours on 7 December 1991. The batch reaction involved the phosgenation of dimethyl aniline (DMA) in a toluene solution. The process involved the addition of 1 tonne of recycled toluene to the reactor, then as no more recycled toluene was available fresh toluene was to be added. Attempts were made to fill the reactor with 2 tonnes of fresh toluene. The flow indicator showed that the required amount of toluene had been added to the reactor, however a control valve between the pump and the vessel was closed and none of the toluene had been added. A level measurement was available for the vessel but as the process appeared to be proceeding normally this was not checked.

The next stage was to add 20 kg of phosgene to check if any water was present in the reactor. This would have resulted in a temperature rise of the solution. Because there was insufficient toluene in the vessel, the temperature indicator was not in the solution and therefore showed no temperature rise. As there appeared to be no water in the reactor, 0.8 tonnes of phosgene were then added to the vessel. After a shift changeover the next steps in the process were carried out. These were to add 1.6 tonnes of DMA and heat to 65°C. The operating temperature was reached but the temperature continued to rise to well above 100°C. As the pressure increased the pressure control valve, pressure relief valve and bursting disc all operated as designed and relieved the vessel to a scrubbing column. The reaction was more violent than had been predicted and the relief system had insufficient capacity to deal with the pressure rise. This resulted in a connection on the condenser line failing and releasing the contents of the vessel to atmosphere. Fortunately the phosgene had been consumed in the reaction. However, the vapour cloud drifted for 4 km affecting about 60 people and staining some property blue.

KEY ISSUES:
• CONTROL SYSTEMS
• REACTION / PRODUCT TESTING
• RELIEF SYSTEMS / VENT SYSTEMS

Report: https://www.icheme.org/media/13702/release-of-chemicals-from-international-biosynthetics-ltd.pdf

Image Credit: HSE